Half-Liter Holdout: 1978 Yamaha XS500E

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1978 Yamaha XS500E
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Laverda 500 Zeta
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Ducati 500 Sport Desmo

1978 Yamaha XS500E
Claimed power: 38hp @ 8,000rpm
Top speed: 107mph(period test)
Engine: 498cc air-cooled, DOHC 8-valve 180-degree parallel twin
Transmission: 5-speed, chain final drive
Weight: 457lb (w/half tank fuel)
Price then/now: $1,589/$800-$2,000

Half-liter bikes have become hot sellers again. Royal Enfield’s new Continental GT is a hit, Harley-Davidson has introduced a new 500 V-twin, and Honda has a trio of 500s; the CB500F, CB500R and CB500X.

The last time the 500cc class was this important was during the disco days of the late 1970s. Then, mid-size motorcycling went multi-cylinder mad: Honda, Suzuki and Kawasaki all offered 3- and 4-cylinder bikes in the 350cc-550cc range. Yet the tuning-fork team stuck to twins: the RD400 2-stroke and the 4-stroke TX/XS500. The long view suggests Yamaha got it right. On balance, two cylinders offered the best compromise of cost versus performance, and the parallel twin offered the most economical and compact package.

Yamaha managed to optimize the parallel twin’s performance while mitigating its chief drawback: vibration. The result was the 1973 double overhead cam, 8-valve, short-stroke TX500 with its 180-degree crankshaft and an “omni-phase” counter-rotating balancer to ensure a smooth running twin.

The technically-advanced engine made lots of power, though almost all of it came between 6,000rpm and the 9,000rpm redline. On early TX models this combined with poor fueling on throttle transitions, light flywheels, uneven power-pulses from the 180-degree crank and excessive driveline lash to make smooth part-throttle and stop-start riding a real challenge. A major maintenance issue emerged, too: The balance shaft drive chain tension required checking and adjusting every 6,000 miles, but to do this meant pulling the alternator, a major service pain. On the plus side, valve lash adjustment was a snap, thanks to forked screw-adjustable cam followers.

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